This CL extends cppgc::DefaultPlatform and TestPlatform to emulate
jobs using std::thread and v8::base::Thread respectively.
Jobs using these platform do not yield unless the job as been
cancelled. Additionally, the job priority is ignored.

Bug: chromium:1056170
Change-Id: I72db1eef410d2be3d3e5ea7d4ece9e5584a451f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416378
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70139}